0
|
1991 Views
|
3 Replies
|
0 Total Likes
View groups...
Share

Syntax Problem?

Posted 10 years ago
 Is somebody able to explain why line 87 works and 85 does not?
3 Replies
Sort By:
Posted 10 years ago
 Hi thanks for the fast Answer Evaluate@ seems to do do the trick. Sorry for the Picture next time I'll post the code. So when do I have to put an Evaluate@ in this situation the problem seems to be at the Integrals.
Posted 10 years ago
 Hi,well, yes. In particular I think that the integration variable of the integrals causes problems. Because of the delayed evaluation it leaves the Integrals as they are. When you plot wrt x then that causes a problem. If you rename the integration variables you also circumvent the problem (but the whole thing gets very slow): a[n_] := (\!$$\*SubsuperscriptBox[\(\[Integral]$$, $$-1$$, $$1$$]$$\*SuperscriptBox[\(Sin[ \*FractionBox[\(Pi\ n$$, $$2$$] y]\), $$2$$] \[DifferentialD]y\)\))^-1 b[n_] := (\!$$\*SubsuperscriptBox[\(\[Integral]$$, $$-1$$, $$1$$]$$\*SuperscriptBox[\(Cos[ \*FractionBox[\(Pi\ n$$, $$2$$] y]\), $$2$$] \[DifferentialD]y\)\))^-1 \[Phi]odd[x_, n_] := b[n] Cos[(Pi n)/2 x] \[Phi]even[x_, n_] := a[n] Sin[(Pi n)/2 x] \[Psi][x_, \[Alpha]_, \[Beta]_] := -\[Alpha] \[Phi]odd[x, 1] + \[Beta] \[Phi]even[x, 2] Plot[{\[Psi][x, 2^-0.5, 2^-0.5], \[Psi][x, 3^-0.5, (2/3)^-0.5]}, {x, -1, 1}] will give the correct plot with no error messages, but it will run for a while. Cheers,M.
Posted 10 years ago
 Hi,I guess that the problem is the delayed evaluation of $\psi$. (BTW, it is quite cumbersome to retype everything if you paste an image into your post. The code would be much easier to debug. a[n_] := (\!$$\*SubsuperscriptBox[\(\[Integral]$$, $$-1$$, $$1$$]$$\*SuperscriptBox[\(Sin[ \*FractionBox[\(Pi\ n$$, $$2$$] x]\), $$2$$] \[DifferentialD]x\)\))^-1 b[n_] := (\!$$\*SubsuperscriptBox[\(\[Integral]$$, $$-1$$, $$1$$]$$\*SuperscriptBox[\(Cos[ \*FractionBox[\(Pi\ n$$, $$2$$] x]\), $$2$$] \[DifferentialD]x\)\))^-1 \[Phi]odd[x_, n_] := b[n] Cos[(Pi n)/2 x] \[Phi]even[x_, n_] := a[n] Sin[(Pi n)/2 x] \[Psi][x_, \[Alpha]_, \[Beta]_] := -\[Alpha] \[Phi]odd[x, 1] + \[Beta] \[Phi]even[x, 2] As you say, if you plot Plot[{\[Psi][x, 2^-0.5, 2^-0.5], \[Psi][x, 3^-0.5, (2/3)^-0.5]}, {x, -1, 1}] that does not work. You can either prefix everything with Evaluate: Plot[Evaluate@{\[Psi][x, 2^-0.5, 2^-0.5], \[Psi][x, 3^-0.5, (2/3)^-0.5]}, {x, -1, 1}] or modify the definition of $\psi$ like so: \[Psi][x_, \[Alpha]_, \[Beta]_] = -\[Alpha] \[Phi]odd[x, 1] + \[Beta] \[Phi]even[x, 2] Now, it's not a delayed definition anymore. Now the plot command works without the Evaluate. Cheers,Marco Attachments: